One state-of-the-art aerating device is known (cf. an advertising prospectus "Brandol area" of Messrs Schumacher GmbH & Co. KG, Germany, 1989) to comprise an air conduit connected to a tubular air distributor provided with radial holes arranged along one of the generatrices thereof. A separate cylinder-shaped dispersing element is held in place above each of said holes, said element being plugged at both ends.
The aforesaid aerating device features a high degree of dispersion of the compressed air fed into the liquid being aerated. However, provision of separate dispersing elements and a sophisticated construction of their attachment to the air distributor affects adversely the operating reliability of the aerating device, because compressed air can make its way into the liquid at the place of attachment of the dispersing element to the air distributor.
Another aerating device we have adopted as the prototype (cf. an advertising prospectus of the Scientific-and-production firm "Ecopolymer" Ltd., entitled "Polymer articles at the service of ecology", 1994) comprises a number of coaxially arranged aerating modules air-tightly held together, each comprising a polyethylene-made perforated tubular air distributor whose outer surface is provided with a double-layer coating of a polymer material, said coating forming a dispersing element. The vacant end of the first module air distributor is provided with a flange for connecting to an air conduit supplying compressed air to the interior of the aerating device air distributors. The dead end of the last module is provided with a blank plug which prevents compressed air against escaping from the interior of the air distributors.
The aerating device discussed hereinbefore operates efficiently when using a few aerating modules (not more than three) interconnected into a string. However, when a greater number of modules is used in a string of the aerating device, a considerable temperature difference of compressed air occurs from the first (relative to the air conduit) module to the last one. Furthermore, an ambient temperature difference is also possible during installation and operation of the aerating device. This in turn leads to thermal deformation of the air distributors interconnected into a string (that is, their elongation or shortening), with the resultant mechanical deformation and breakage of the air distributors, whereby the intactness of the dispersing coating is upset and hence the operation of the aerating as a whole is disturbed as well.